Heating and cooling systems are known, which comprise at least one load circuit, through which fluid as a heat transfer medium flows. This can be water for example. Such a system can for example be provided as a heating installation in a building, wherein preferably several load circuits are present. The load circuits are switched on and off in the known manner in dependence on the room temperature, which can be effected for example via room thermostats. Thus, in the case of a heating system, the load circuit is switched on when falling short of a desired temperature and the load circuit is switched off on exceeding or reaching a desired temperature.